This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-149529 filed on May 18, 2001.
1. Field of the Invention
The present invention relates to a thermopile infrared sensor, which is used in temperature measurement, image recognition, or the like.
2. Description of Related Art
A thermopile infrared sensor is a sensor that produces an output upon receiving infrared radiation. Such a sensor can be inspected while it is in a wafer state by applying infrared radiation onto the sensor and measuring an output of the sensor. However, the output substantially varies from sensor to sensor. Thus, it is difficult to detect circuit failure, such as short circuit, based on the output of the sensor. For example, even when five thermocouples out of one hundred thermocouples in a single sensor are defective due to short circuit, the remaining ninety five thermocouples outputs normally. Thus, this defective sensor can still produce 95% of the output of the normal sensor, and this value may fall within an allowable variation range. As a result, the defective sensor is likely to be shipped to a next manufacturing stage.
The present invention addresses the above disadvantage. Thus, it is an objective of the present invention to provide a thermopile infrared sensor, which allows more reliable detection of circuit failure of the sensor, such as short circuit of the sensor, while the sensor is still in a wafer state. It is another objective of the present invention to provide a method for inspecting such a thermopile infrared sensor.
To achieve the objective of the present invention, there is provided a thermopile infrared sensor including a semiconductor substrate and a series circuit formed on the semiconductor substrate. The series circuit includes first and second end terminals, a set of thermocouples electrically connected in series between the first end terminal and the second end terminal, and at least one electrical inspection terminal. The at least one electrical inspection terminal extends from a corresponding intermediate point in the series circuit between the first end terminal and the second end terminal to divide the set of thermocouples into at least two groups of thermocouples and to allow inspection of each group of thermocouples. The set of thermocouples includes dissimilar electrically conductive materials, which are alternately electrically connected in series on the semiconductor substrate such that a plurality of hot junctions and a plurality of cold junctions are alternately formed by the dissimilar electrically conductive materials.
Each hot junction shows a substantial temperature increase upon absorption of infrared radiation while each cold junction shows little or no substantial temperature increase upon absorption of the infrared radiation. An electromotive force generated by a difference in temperature between each of the hot junctions and adjacent one of the cold junctions is outputted from the series circuit through the first and second end terminals.
TO achieve the objective of the present invention, there is also provided a method for inspecting a thermopile infrared sensor having a series circuit. The series circuit includes first and second end terminals, a set of thermocouples electrically connected in series between the first end terminal and the second end terminal, and at least one electrical inspection terminal, which extends from a corresponding intermediate point in the series circuit between the first end terminal and the second end terminal to divide the set of thermocouples into at least two groups of thermocouples. The method includes steps of measuring a resistance value of each group of thermocouples through adjacent two of the first and second end terminals and the at least one electrical inspection terminal while the thermopile infrared sensor is in a wafer state, and determining whether the thermopile infrared sensor is normal based on the measured resistance value of each group of thermocouples.